high memory usage HA cluster

hello

we have 2 sophos utm 220 appliances
running in HA cluster warm standby
currently we are running 9.002

2 processes relating to postgres are using respectively -
27% slon asg_cluster dbname=reporting user=ha_sync
19% slon asg_cluster dbname=hotspot user=ha_sync

we are using
router ips wireless and vpn
over time the memory usage increases till it gets to 80-85% then the boxes start swapping - up to 40%

the same thing happened when we were running code 9.001
the reboot / upgrade basically reset the ram to a lower amount then it builds up again over time

i don't see anyone reporting the same problem so i'm wondering if its a config problem ?